This invention relates to the production of long chain tertiary amines by reductive amination of C.sub.10 -C.sub.26 alkyl ketones with secondary amines. More particularly, it relates to a process for the reductive amination of C.sub.10 -C.sub.26 dialkyl internal ketones to obtain tertiary amines in high yield. Still more particularly, it relates to the reductive amination of said ketones with secondary amines using a supported nickel catalyst.
The preparation of tertiary amines by the general process of reductive alkylation of ketones and aldehydes with amines is well known and has been thoroughly reviewed in Organic Reactions, Volume 4, chapter 3 (1948). Reductive amination is accomplished by reacting the aldehyde or ketone with the amine and hydrogen in the presence of a supported metal catalyst, the metal being, for example, nickel or a noble metal such as platinum or palladium. Primary emphasis is on the reaction of low molecular weight aldehydes and ketones with ammonia and low molecular weight amines, using mainly platinum as the catalyst. The preparation of tertiary amines by the reaction of ketones and secondary amines is disclosed, using a platinum catalyst, with yields up to about 47% of the theoretical amount.
From the discussion and data presented in Organic Reactions, Volume 4, it appears that reductive amination with secondary amines, using platinum or palladium catalysts, gives rather low yield of product tertiary amine. On page 207 of said reference, a tabulation is set out showing alkylation of various ketones with methyl-sec.butyl amine. With acetone the yield of tertiary amine product is 47%. A sharp decline in yield is observed as the molecular weight of the methyl ketone reactant is increased such that for methylethyl ketone the yield is 18%, for methyl-n-butyl ketone the yield is 8% and for 2-octanone the yield is merely 0.6%. Thus, for methyl ketones, it would appear that the reductive amination reaction to obtain tertiary amines provides satisfactory yields only for the extremely low molecular weight ketones.
If one wishes to obtain tertiary amines from internal ketones, i.e., high alkyl ketones in which each alkyl group has 2 or more carbon atoms, the process taught in Organic Reactions, Volume 4, would appear to be virtually useless. The reaction of methyl-sec.butyl amine with diethyl ketone, the lowest molecular weight internal ketone, using a platinum catalyst results in tertiary amine of only 0.02% yield.
Accordingly, it is an object of this invention to develop a process for the preparation of tertiary amines by the reductive amination of internal ketones having from 10 to 26 carbon atoms, particularly those having from 10 to 13 carbon atoms. It is a further object to develop such a reductive amination process with sufficiently high product yield so as to be commercially feasible.